Method of disposing of carbon dioxide

ABSTRACT

A process and also an arrangement for disposing of one of more carbon dioxide-containing fractions which occur at one or more sites of a fractionation and/or liquefaction process such as, for example, a natural gas liquefaction process. The carbon dioxide-containing fraction(s) is or are subjected to a purification (B) and/or liquefaction (C) and subsequently sequestered (D). Preferably, use is made of at least one substream ( 6 ) of the liquefied carbon dioxide-containing fraction(s) as refrigerant (D) within the fractionation and/or liquefaction process.

The invention relates to a method and also an arrangement for disposing of one of more carbon dioxide-containing fractions which occur at one or more sites of a fractionation and/or liquefaction process such as, for example, a natural gas liquefaction process.

In the context of fractionation and/or liquefaction processes such as, for example, natural gas fractionation and/or liquefaction processes, generally one or more carbon dioxide-containing fractions occurs or occur. Such “carbon dioxide sources” are, for example, the residual gas originating from acid gas removal or amine scrubbing and also the exhaust gas streams of gas turbines and steam generators. The abovementioned carbon dioxide-containing fractions have been to date released essentially untreated to the atmosphere. The reason for this is to be seen in the fact that although limiting values are prescribed for hydrocarbons and sulphur compounds by the German TA Luft [German Instructions on Air Pollution], they are not for carbon dioxide; emission thereof is therefore still permitted without restrictions. In view of current discussions with respect to the carbon dioxide problem, such a procedure can now be considered outmoded.

In a multiplicity of liquefaction and/or fractionation processes, carbon dioxide is used as refrigerant. In particular in natural gas liquefaction processes, pure carbon dioxide refrigerant cycles are suitable for precooling the natural gas to be liquefied; such a natural gas liquefaction method is disclosed, for example, in U.S. Pat. No. 6,722,157. Provision and, in particular, disposal of the carbon dioxide necessary for these (precooling) refrigerant cycles, however, have not to date been given sufficient attention.

It is an object of the present invention to specify a method of the type in question and also an arrangement of the type in question for disposing of one or more carbon dioxide-containing fractions which avoid the above-described disadvantages.

To achieve this object, a method of disposing of one or more carbon dioxide-containing fractions is proposed which is characterized in that the carbon dioxide-containing fraction(s) is or are subjected to a purification and/or liquefaction and subsequently sequestered.

The arrangement of the invention for disposing of one or more carbon dioxide-containing fractions is characterized by at least one purification unit and/or at least one liquefaction unit to which is or are fed the carbon dioxide-containing fraction(s), and also by means for feeding the purified and/or liquefied carbon dioxide-containing fraction(s) to a sequestration.

Further advantageous embodiments of the method of the invention and also of the arrangement of the invention for disposing of one or more carbon dioxide-containing fractions which are subject matters of the dependent claims are characterized in that

-   at least one substream of the liquefied carbon dioxide-containing     fraction(s) is used as refrigerant within the fractionation and/or     liquefaction process, -   the liquefied carbon dioxide-containing fraction(s), before     sequestration thereof, is or are pumped to a pressure of at least     100 bar and -   the carbon dioxide-containing fraction(s) has or have a carbon     dioxide content of at least 90% by volume.

The method according to the invention and the arrangement according to the invention for disposing of one or more carbon dioxide-containing fractions expansion turbine, and also other embodiments of the same may be described in more detail hereinafter with reference to the exemplary embodiment shown in the FIGURE.

The black boxes A, A′ and A″ shown in the FIGURE represent a plurality of “carbon dioxide sources” such as, for example, one or more amine scrubbers (A), one or more gas turbines (A′) and also one or more steam generators (A″), as are generally provided in the context of fractionation and/or liquefaction processes.

The carbon dioxide-containing gas or exhaust gas occurring in these “carbon dioxide sources” is taken off for lines 1, 2 and 3, combined and fed via a shared line 4 to a purification unit B. This purification unit B is preferably constructed as a purification unit operating by absorption, adsorption and/or permeation. The purification unit B comprises, where this is necessary in individual cases, a drying unit for the carbon dioxide-containing fraction which is fed. The carbon dioxide-containing fraction taken off from the purification unit B via line 5 preferably has a carbon dioxide content of greater than 90% by volume.

This fraction is then compressed to the extent that, in the downstream liquefaction unit C, liquefaction of the carbon dioxide-containing fraction can proceed against a suitable medium, such as, for example, cooling water, air or another suitable fluid.

The liquefied carbon dioxide-containing fraction can then according to the invention be used in whole or at least in part as refrigerant, for example for precooling in the context of a natural gas liquefaction process, or for cooling in the removal of lighter hydrocarbons, such as C₂₊ or C₃₊ hydrocarbons, from natural gas. This (pre)cooling is intended to be shown by black box D to which the carbon dioxide-containing fraction is fed via line 6.

The carbon dioxide-containing fraction used as refrigerant (black box D) and “exhausted” is fed via line 7 back to the liquefaction unit C and in this is optionally reliquefied.

The fraction of liquefied carbon dioxide-containing fraction which is intended to be fed to a sequestration is pumped to the desired sequestration pressure by means of a single-stage or multistage pump unit 9. This sequestration pressure is preferably above 100 bar. The carbon dioxide-containing fraction is fed via line 8 to a suitable sequestration E such as, for example, a subterraneous store or cavern.

The method according to the invention and also the arrangement according to the invention for disposing of one or more carbon dioxide-containing fractions is suitable, in particular, for floating natural gas production plants since, in these, owing to the safety risks associated with certain hydrocarbon mixtures, carbon dioxide is preferred as refrigerant for the precooling. Advantageously, the invention is always used when, firstly, within the fractionation process and/or liquefaction process, a plurality of carbon dioxide-containing fractions occur, and secondly, liquid carbon dioxide or a liquefied carbon dioxide-containing fraction is desired or necessary as refrigerant. 

1. A method of disposing of one or more carbon dioxide-containing fractions which occur at one or more sites of a fractionation and/or liquefaction process, such method comprising subjecting the carbon dioxide-containing fraction(s) a purification (B) and/or liquefaction (C) and subsequently sequestering resultant carbon dioxide-containing fraction (D).
 2. A method according to claim 1, comprising passing at least one substream (6) of the liquefied carbon dioxide-containing fraction(s) as refrigerant (D) within the fractionation and/or liquefaction process.
 3. A method according to claim 1, wherein the liquefied carbon dioxide-containing fraction(s), before sequestration (D) thereof, is or are pumped (9) to a pressure of at least 100 bar.
 4. A method according to claim 1, wherein, the carbon dioxide-containing fraction(s) has or have a carbon dioxide content of at least 90% by volume.
 5. An arrangement of apparatus for disposing of one or more carbon dioxide-containing fractions which occur at one or more sites of a fractionation and/or liquefaction plants, comprising at least one purification unit (B) and/or at least one liquefaction unit (C) which is or are connected in fluid communication to means for feeding the carbon dioxide-containing fraction(s), and means for feeding resultant purified and/or liquefied carbon dioxide-containing fraction(s) to means for sequestration (D).
 6. An arrangement according to claim 5, wherein the means for feeding the purified and/or liquefied carbon dioxide-containing fraction(s) to a sequestration (D) comprises at least one pressure-boosting unit (9).
 7. An arrangement according to claim 6, wherein the pressure-boosting unit (9) has means to increase the pressure of the carbon dioxide-containing fraction(s) fed to the means for sequestration (D) to at least 100 bar.
 8. A method according to claim 1, wherein said sites include a natural gas liquefaction process. 